@lumi Android's hardware-based attestation API would not cause these issues if it only had the pinning-based attestation we use as the basis for Auditor and omitted root-based attestation. The issue is having attestation roots which determine which hardware and operating systems are valid. Hardware-based attestation can be provided without any centralized authority determining which hardware and software is valid. It would still provide nearly all of what our Auditor app uses without roots.

@lumi We support hardware-based attestation based on pinning for protecting users against attacks. Root-based attestation has extremely weak security due to depending on the entire ecosystem of devices not having vulnerabilities enabling leaking keys chaining up to the root. Pinning-based attestation can be used as a very strong security feature. Check out our Auditor app. It does use the root-based attestation for first verification but it would provide most of what it does without it.

@lumi GrapheneOS supports the Android hardware-based attestation API. The API itself is a neutral approach which can support arbitrary roots of trust, non-stock operating systems verified based on verified boot key fingerprint and also has pinning-based attestation based on a proposal we made to Google before they stopped collaborating with us. Pinning-based attestation can be used with or without chaining up to a root for bootstrapping trust. It could exist without root-based attestation.

@lumi The problem with the Android attestation API is that the documentation and libraries treat Google as the only root of trust and it's also inherently biased towards stock operating systems since it can verify those by simply checking for the green state instead of needing to allowlist keys for the yellow state. Even if apps used hardware-based attestation instead of the Play Integrity API, many wouldn't permit GrapheneOS and they'd still be limiting what people can use if they did allow it.

@lumi Apps wouldn't be able to disallow using operating systems via the hardware attestation API if it only supported pinning-based security and didn't have support for chaining up to a root. It's chaining up to a root which enables trusting only Google's root or specific roots permitted for specific alternate hardware. Similarly, there's the fact that they differentiate green and yellow where green trusts every OS approved by the root CA party vs. yellow requiring allowlisting fingerprints.

@lumi These attest keys are meant to be pinned after the initial use and then used to enforce that subsequent attestations have trust chained from the initial verification. As long as the initial key was securely generated in the TEE or secure element and those have not been compromised with exploits then compromised apps or a compromised OS cannot fake the data. It chains trust from an initial starting point and does not limit which hardware or software can be used, the root approach does.

@lumi Yes, and the attestation metadata includes certain information set by the OS developers such as the patch level for the OS. As an example of how this can be used, consider 2 people talking to each other on Signal who both want it to be a highly secure conversation. There could be a way to opt-in to sending each other attestations as part of the verification. It could then enforce that it's the same devices talking to each other and that the patch level continues to be updated, etc.

@lumi As an example, pretend that one of the 2 devices is compromised and the attacker stops allowing security patches. This would be visible in the attestation metadata and the attacker wouldn't be able to fake it without an early boot chain or secure element exploit. It could similarly provide more than it does today such as warning if the device hasn't been rebooted for a certain amount of time. This would all work fine without root-based attestation. Our Auditor app provides this stuff.

@lumi Most of the companies using attestation want root-based attestation. They primarily want to use it to control which hardware and software people can use. Useful hardware-based attestation can be provided without enabling apps to do this. It can also be useful without being available to user installed apps but it's not harmful for it to be available to user installed apps if it doesn't provide a root-based system that's inherently anti-competitive. It's even actually very anti-security.

@lumi Disallowing people using GrapheneOS is anti-security and that's exactly what apps using either the Play Integrity API or Unified Attestation API are going to be doing. Both are going to be allowing extremely insecure options without basic patches and protections but yet not permitting a hardened OS with much better security. As far as we're concerned the whole approach is both fraudulent and violates antitrust law. Fighting Google's influence is hard but fighting this won't be hard.